BackgroundThe differential diagnosis of bilateral lung infiltrates and prognosis prediction can be challenging for clinicians in the intensive care unit (ICU). We analyzed the proteome from bronchoalveolar lavage fluid (BALF) and determine their usefulness for evaluating the infectious causes and mortality associated with bilateral lung infiltrates.MethodsIn the ICU cohort, 136 patients with bilateral infiltrate on chest radiographs were selected, and bronchoscopy with bronchoalveolar lavage (BAL) was performed. Proteomics profiling of the exosomes in the BALF (n=20) was conducted to identify candidate protein biomarkers potentially associated with infection or mortality. The BAL samples (n=116) were used to measure the candidate biomarker levels.ResultsThe candidate biomarkers, CD20, CLIC4, SCFD1, and TAP1, were selected for the differential diagnosis of infection or mortality. The levels of CD20 were significantly elevated in patients with non-infectious causes compared to those with infectious causes (248.6±154.5versus177.6±150.9 ng·mL−1, p=0.014). The levels of CLIC4, SCFD1, and TAP1 did not differ between the two groups. As per the receiver operating characteristic analysis, CD20 was a significant predictor of non-infectious causes (area under curve, 0.668; 95% CI, 0.567–0.769; p=0.002; cut off value, 167.6 ng·mL−1; sensitivity, 74.1%; specificity, 63.2%). There were no significant differences in the concentrations of the biomarkers between survivors and non-survivors.ConclusionsOur results suggested that CD20 levels in BALF might be a useful biomarker for differentiating non-infectious and infectious diseases in patients with bilateral lung infiltrates.